Device and method for mapping of visual scene onto projection surface

ABSTRACT

A system and a method for determining an optical parameter distribution at a projection surface are provided. The system comprises a visual field sensor. The visual field sensor is configured to measure a visual field of a user related to a specific vision task in a visual field of a user. The visual field sensor is further configured to determine gaze directions of the user during the specific vision task. The system comprises a head orientation and/or position sensor. The head orientation and/or position sensor is configured to measure head orientation and/or position of the user in relation to the visual field during the specific vision task. The system is configured to enable computation of the user&#39;s eye orientation in relation to the head of the user based on the gaze directions of the user and the head orientation and/or position of the user to determine an optical parameter distribution at a projection surface between the visual field and a retina of the user.

Examples relate to concepts for customizing optical aids andapplications thereof and in particular to a system and method fordetermining an optical parameter distribution at a projection surface.

Presbyopia is a condition developed with the natural aging of the eyewhich manifests itself as a worsening ability to accommodate the lens ofthe eye. The typical onset is above 35 years and this condition developsprogressively until complete cessation of accommodation abilities.Multiple solutions have been developed through human history withsignificant progress achieved in the recent decades. The most commonremedy is reading eyeglasses, which are used for near tasks. The readingeyeglasses artificially extend the accommodation range of the eye. Auser requiring vision correction for far vision as well (e.g. due tomyopia) is required to wear at least two pairs of spectacles and changethem based on the required task. This may be inconvenient.

Thus, the user may use glasses having multiple optical powers. This canbe achieved by geometrically separating zones of different opticalpower, such as in bifocal and trifocal glasses. The user of such glasseshas an option to select the required optical power by looking on theobject of interest through a required zone. The positions of therespective zones are selected based on a natural correlation of tasksand eye angles: the higher power is typically located in the lower zone(near zone), since the near vision tasks are typically performed byaligning the object in the lower gaze zone (such as reading,smartphones, etc.). The upper zone is thereby reserved for the farvision tasks (far zone). In trifocal glasses, an intermediate zoneexists between near and far zones to support vision in middle range.Further to that, progressive addition lenses exist which do not havevisible lines separating respective optical power zones and instead havesmooth transitions from one zone to another.

Since such a spatially separated corrective solution is neither naturalnor intuitive for human eyes, the user must adapt thereto. Specialconsideration takes fitting the zones to the requirements of theparticular user in order to minimize possible disruption of the user'sviewing habits developed through lifespan. Thus, preferably a correctivesolution has to be adapted to the individual visual behaviour. Suchcustomization could include optimal mapping of optical powers and/orother optical parameters to the surface of an optical aid, such asspectacles. The terms customization, individualization andpersonalization are further used interchangeably. The optical aid mayalso be called vision aid or visual aid herein. The optical aid may bean additional/enhancing optical element to the natural visual system ofan eye, such as spectacles, contact lenses, augmented or virtual realityheadsets, retinal or other visual implants, corneal inlays, etc. Theoptical aid may be a replacement of the natural element of the visualsystem, such as intraocular lens as a replacement of the natural lens.The optical aid may be a modification of the element of the visualsystem, such as refractive surgery performed on the cornea or on thelens. The optical aid may be a combination of forms of optical aids.

Understanding of lens position in the finished optical aid in relationto the user's eyes is important, if not essential for customization.Further to that, understanding the user's visual behavior is important,if not essential. This includes how the user typically positions objects(related to specific vision tasks) in his/her visual field and how theuser positions his/her body, head and eyes in relation to the objectsrelated to the specific vision tasks.

An exemplary vision task is reading. A handheld media (for example bookor electronic device) is typically positioned in such a way that thehead is inclined roughly half-way to the object, while the remainingrequired inclination angle is adjusted by the eyes themselves. Thedifference between the head's inclination angle and the eyes'inclination angle is individual as well as the positioning of the mediain the visual field.

It is thus critically important to understand the preferred anglebetween the user's gaze/eyes/head in order to better customize adistribution of visual zones at the optical aid.

Optical aids may have to be optimized with respect to user-specificpreferences.

Such a demand may be satisfied by the subject-matter of the claims.

According to a first aspect, a system for determining an opticalparameter distribution at a projection surface is provided. The systemcomprises a visual field sensor. The visual field sensor is configuredto measure a visual filed of a user related to a specific vision task,for example identify an object related to the specific vision task inthe visual field of the user. The visual field sensor is furtherconfigured to determine gaze directions of the user during the specificvision task. The system comprises a head orientation and/or positionsensor. The head orientation and/or position sensor is configured tomeasure head orientation and/or position of the user in relation to thevisual field during the specific vision task. The system is configuredto enable computation of the user's eye orientation in relation to thehead of the user based on the gaze directions of the user and the headorientation and/or position of the user to determine an opticalparameter distribution at a projection surface between the visual fieldand a retina of the user.

An optical parameter may be a distance to an object related to thevision task, which may be mathematically linked to the optical power ofthe optical aid. The optical parameter may be a luminance of the objectof the vision task, which may be linked to the pupil size of the eyeduring the specific vision task. The optical parameter may be a spectralcontent of light originating from the object related to the vision task.The optical parameter may include an angular distribution of light fielddetected from the visual field. The optical parameter may include apolarization state and polarization degree of light detected from thevisual field.

Thus, instead of direct monitoring of the eyes' movements of the userand viewing directions for a specific vision task, the eyes' movementsof the user with respect to the head movements can be calculated fromthe head and gaze angles. Directly monitoring the eyes' movements needsto be performed in familiar settings of an everyday routine of the userand may need sufficient statistics to be accumulated in long-termcontinuous measurements in order to obtain reliable estimates. However,long term monitoring of the eyes' movements of the user can bedisadvantageous due to the cumbersomeness of the existing eye-trackingsolutions, alignment requirements and battery consumption of theequipment. This can be avoided by a system according to the firstaspect.

The visual field sensor may be configured to measure at least oneparameter of the visual field. The parameter of the visual field may bemeasured with at least a single dimensionality. For example, theparameter may be resolved in a polar coordinate system along at leastone angle of rotation, such as pitch (inclination, rotation aroundhorizontal axis of the sensor), yaw (rotation around vertical axis) orroll (rotation around transverse axis) angles. Additionally oralternatively, the parameter of the visual field, i.e. the visual fieldparameter, can be resolved in a cartesian coordinate system along theposition coordinates.

Additionally or alternatively, the visual field sensor may be configuredto measure the visual field parameter in two or three dimensions. Theparameter of the visual field may be at least one of the following:distance to the objects of the visual field; intensity, spectralproperties, polarization parameters (e.g. degree of polarization, Stokesparameters) and/or light-field parameters of light emitted and/orreflected by objects of the visual field.

The visual field sensor may be further configured to enabledetermination of gaze direction. This can be achieved in multiple ways.In one simple example, the visual field sensor may comprise or be adirectional sensor mounted on the spectacles and directed forwards andcoaligned with the optic/optical axis of spectacles. The directionallight sensor may be based on optics or be light based. The directionalsensor may also be any kind of directional distance sensor, for exampleRADAR or LIDAR. The directional sensor may be capable of moving togetherwith the spectacles. The system may also comprise the head orientationsensor aligned with the spectacles or other device, the system can bemounted on. Due to the natural head movements of the user, thedirectional sensor may be capable of sampling an environment indifferent directions; in combination with the head orientation sensor,the system may allow obtaining an angle-resolved image of lightningconditions.

When the user is reading content on a handheld electronic device with anilluminated screen (e.g. smartphone or a tablet), the directional sensormay be configured to detect the light emitted by the device. Due to headdynamics, the directional sensor may be configured to occasionallydetect light emitted from the device.

Corresponding inclination angles α indicate the gaze directions. At thesame time, during reading activity, a head orientation, for example thehead pitch angle, may in average equal β. Angle β may be typically lowerin absolute value than the gaze angles α. The eye angle can be found asα-β. In this way, knowing the type of vision activity, object of visionactivity may allow estimating the eye angle from gaze and headorientation.

The visual field sensor may use the directional sensor, also coalignedwith the optic/optical axis of spectacles. Due to the natural headmovements in combination with measurements of the head/deviceorientation sensor, a map of distances to the surrounding objects can beconstructed. This can also be performed by the processing unit, asintroduced below. By knowing a priory the type of vision task, the usercan identify the handheld device as an object located in a vicinity ofthe user (for example by a user input). Further analysis may beperformed in a way similar to the example above.

The directional sensor may be tilted downwards in relation to theoptical axis of spectacles in order to collect more measurements fromthe handheld media. For example, for a typical gaze inclination duringreading of handheld media of 30°, it is advantageous to tilt thedirectional visual field sensor downwards by the same angle in order toincrease the sampling density from the object of vision activity(handheld media or device) in the typical case. This may be achieved bypermanently directing the visual field sensor downwards. Alternativelyor additionally, the system may comprise at least two directionalsensors, at least one of which may be directed downwards by a requiredangle. The system may be configured to enable or disable directionalsensors based on the identified vision activity.

Alternatively or additionally, the system may be configured to changethe direction of the visual field sensor in order to optimise thedensity of data based on the visual activity/task performed by the user.In one implementation, the visual field sensor may be configured to usea scanner to sample the parameter of the visual field in differentdirections. Based on the identified activity, the density of samplingmay be adjusted to obtain more samples of the object of interest such asobject of vision activity.

The specific vision task may be understood as the activity related tovision which is characterized by the relative consistency of the visualfield, for example reading, writing, driving, using handheld devices orwatching TV. The vision task may also be selected beforehand, whileperforming the task or later.

The system may be configured to perform measurements of a singleactivity, such as reading. In this case the object, acquired by thevisual field sensor, may be known a priory as reading media/material(such as book or handheld device) and thus the majority of the sensormeasurements are related to the reading material. In this example,processing of the data can be performed with simple statistical methodsmeant to discard outliers, in particular, robust statistical processing.In a similar fashion, the measurements of the head orientation sensormay correspond to the head orientation of reading activity and thusprocessing can be performed with a method of reduced complexity, such assimple statistical methods.

The system may comprise a user input which may enable the user toindicate the vision task and/or the object related to the vision task.The user input may be implemented on the device itself or on anaccompanying computing device, such as a mobile phone or a mobilecomputer. Further, the user input may be implemented on a cloudinterface.

The visual field sensor may be configured to identify an object of thevisual field of the user related to the specific vision task. Further,the visual field sensor may be configured to derive the gaze directionsof the user related to the identified object of the visual field.

The system may further comprise a context sensor. The context sensor maybe configured to measure at least one parameter related to an activityof the user.

The system may further comprise a statistical classifier. Thestatistical classifier may be part of the processing unit as describedbelow. The statistical classifier may be configured to identify thevision task and/or object of the visual field of the user from at leastone of the visual field sensor, the head orientation and/or positionsensor, and the context sensor. Identification may be at least in partperformed automatically, for example with methods of statisticalanalysis/modelling.

The context sensor may be adapted to measure at least one contextparameter related to the vision task of the user. The context sensor maybe adapted to enable the system to derive statistical characteristics ofthe measured context parameter to be compared with statisticalcharacteristics of a signature context parameter associated withspecific vision tasks. These statistical characteristics of the measuredcontext parameter may be stored on or in a memory unit. The memory unitmay also include the signature statistical characteristics of thecontext parameter (stored beforehand).

The system may further comprise a memory unit such as the aforementionedmemory unit. The memory unit may be configured to store the headorientation and/or position, in particular head angles, and the gazedirections, in particular gaze angles, both related to the specificvision task. The head angles and the gaze angles may be stored duringthe time of performing the specific vision task. The stored headorientation and/or position, in particular the stored head angles, andthe stored gaze directions, in particular gaze angles, may form thebasis for determining the optical parameter distribution at theprojection surface between the visual field and the retina of the user.

In consequence, the information about the optical parameter distributionmay be stored for later customization of an optical aid for the user.

The system may further comprise a processing unit. The processing unitmay be configured to determine the corresponding differences between thehead orientation and/or position, in particular head angles, and thegaze directions, in particular gaze angles, and to determine the opticalparameter distribution at the projection surface between the visualfield and the retina of the user.

The processing unit may be configured to determine the correspondingdifferences between the stored head orientation and/or position, inparticular head angles, and the stored the gaze directions, inparticular gaze angles, and to determine the optical parameterdistribution at the projection surface between the visual field and theretina of the user.

In consequence, the optical aid for the user can be customized straightaway after simple use of the system.

The processing unit may be connected to the memory unit. Further, thememory unit may be interleaved such that the processing unit maycomprise its own integrated memory. Computation may then be performed onthe processing unit promptly or after a measurement session has beenperformed by the user. Thus, the user may be provided with promptadaptation/customization of his/her optical aid or the results may bestored for the option to gather data for longer assessing the user inorder to provide optimal customization of the optical aid.

These signature statistical characteristics associated with the contextparameter may be fed to the memory unit beforehand, during or aftermeasuring the context parameter. The memory unit and the context sensormay thus be in direct communication with each other. This also appliesto the processing unit which may perform the correlation/comparison ofthe respective statistical characteristics.

The context parameter may be a metric of motion of the user, forexample, motion intensity, amount of acceleration, direction ofacceleration, amount and/or direction of rotation. The context parametermay also be an illumination condition, such as light intensity,direction and spectral content, presence of flickering and it'sfrequency. The context parameter may be a location and orientation ofthe user, estimated with location and positioning methods, such asglobal and local positioning systems, wireless signal quality, etc. Thecontext sensor may include an imaging system configured to obtain imagesof the visual field as well as surrounding of the user and/or userhimself/herself.

The context sensor can be a wearable camera. Alternatively oradditionally, the camera is mounted outside of the users' body. Forexample, the camera may be a camera of a device, like mobile phone,handheld computer, tablets, laptop and desktop computer, or can be aseparate camera module placed on the desktop.

The context sensor may be a microphone configured to measure acousticvibrations (sound) around user. Intensity, spectral content and patternmay be used as context parameters. The context sensor may be equippedwith the detector of electromagnetic radiation in radio frequency rangeto enable detection of signals from wireless radio emitters. Forexample, the radio waves of GSM, GPS, WiFi, Bluetooth can be used.

Additionally or alternatively, the system may be configured to detectsignals of wireless emitters. The system may be equipped with anelectromagnetic receiver configured to receive signals. Such signals maybe communicated by means of electromagnetic waves (radiowaves and/orlight) and/or by mechanical waves. The system may be equipped with anelectromagnetic transmitter configured to transmit signals in order torequest additional information from surrounding devices. For example, aBluetooth communication module of a car may be used to identify adriving activity. Further, radiation of the Bluetooth module of asmartphone or a tablet may be used to identify the activity of using ahandheld device. Since Bluetooth modules typically broadcast thenumerical (MAC address) and text identifiers of the device, a databasecan be used to associate the device with a specific activity. Forexample, the car may broadcast the text identifier of the car model andmaker, while the smartphone by default may broadcast a maker and modelof the phone, which may be associated with activity. The additionalinformation, such as identifier of the device or device location ordevice type may be requested by the system by transmitting requestsignals by means of a transmitter. The properties of the signal, such assignal strength, signal delay, signal reflections may be used to improveclassification of vision activity.

The context sensor may be equipped with the positioning/location sensor,configured to provide information about the position and movement(speed, acceleration and trajectory) of the user. The positioning sensormay be one of global positioning systems, like GPS, GLONASS, GNSS, orlocal positioning systems or indoor positioning systems. The indoorpositioning system may be implemented by scanning wireless devicesaround the system, for example WLAN or Bluetooth emitting devices.Position and movement of the user may be used by the classifier toclassify the corresponding activity. For example, the user walks.Combining this information with the motion data showing a characteristicwalking pattern, the classifier may conclude that the user is walking.

The visual field sensor as well as the head orientation/position sensorcan be used as a context sensor as well.

The context parameter measured by the context sensor may be used forautomatic identification of vision task in combination with at least oneother context parameter, different from the first one and measured withthe same or different context sensor. At least two context parametersfrom the same or different context sensors can be used together for theidentification of activity/task or the object related thereto.

The vision task may be identified automatically based on at least one ofthe visual field parameter measured by the visual field sensor,characteristic points cloud, head orientation, movement pattern,illumination conditions and context sensor readings. Identification ofactivity/task, or classification may be performed using statisticalanalysis of data, for example by methods of machine learning withclassifier trained on the data measured during known/labelled or taggedactivities. Such methods may include logistic regression, naïve Bayesclassifier, Fisher's linear discriminant, support vector machines,k-nearest neighbour, decision trees, random forests, neural networks, orany other known method or combination of multiple methods.

The data of the visual field sensor can be used in originaldimensionality and resolution or can be reduced to improve the stabilityof an underlying classification algorithm. For example, the visual fieldsensor utilizing the directional sensor may construct the map of objectsof the visual field. For example, handheld reading material, such asbook, tablet or smartphone may be recognized as a points cloud forming aplane with known size in two-dimensional or three-dimensional map. Whenthe object of matching shape and size is detected, accompanied bycharacteristic head tilt, the reading of handheld media may be detected.

Additional sensors may improve the accuracy and specificity ofclassification. For example, a sensor capable of detecting apolarization state of reflected light may be used to differentiateliquid crystal based display of the handheld electronic devices from thepaper-based media such as books. Additionally or alternatively, thedirectional sensor may be used to detect light emitted by electronicdevices to achieve the same. Additionally or alternatively, a motionsensor may be configured to detect head movements associated withreading in order to differentiate reading of handheld material fromwatching media content, such as movies on handheld electronic devices.Additionally or alternatively, a light sensor capable of detectingtemporal variations of light caused by dynamic media content, such as amovie, may be used to enable differentiation of reading and watchingactivity.

The system may include a database of original measurements orstatistically processed measurements performed during knownactivities/tasks. Thus, unknown activity/task can be identified bycomparing measurements with the measurements from the database. In asimilar way, identification of the object in the visual field may beperformed automatically with methods of statistical analysis/modelling.The database of signature measurements of known objects may be composedand further object identifications may be performed by comparingmeasurements of unknown objects with the measurements of known objectsstored in a database.

The visual field of a user may be defined as the field of view of theuser. The user may be a patient or a wearer of an optical aid, such aslenses, spectacles, or someone who is to receive a modification orreplacement of an optical element of an eye. The optical aid may also bea device which primary aim is not to compensate insufficiencies ofvision but to enhance vision with elements beyond the function of thenormal human vision. For example, such enhancement can be provided withthe virtual/augmented/mixed reality headset or smart glasses, whichmodify the normal visual field in order to provide extra functionality,such a display of elements of graphical user interface, highlighting ofobjects in visual field, adding artificial objects to the visual fieldand so on. It is to be understood that such device may still providecompensation of vision insufficiencies such as myopia, hyperopia,presbyopia and others.

The gaze direction is defined by the direction to the point which isviewed by the eyes from a common coordinate axis. The gaze direction mayalso be understood as gaze angle. In two-dimensional view, whenbilateral symmetry of the visual task/activity can be assumed, thecommon coordinate axis may be the horizontal plane and the gaze angle isdefined by a single pitch angle. The gaze angle may be constructed by aninclination angle of the head (head pitch angle) and an inclinationangle of the eyes with respect to a head angle.

The gaze direction/angle may be derived from a position of the objectrelated to the visual task in a common coordinate system. The commoncoordinate system may be a spherical coordinate system. The sphericalcoordinate system may have its origin at a root of a nose or anotherpoint of the user.

The projection surface may be defined as a surface related to thefunction of the optical aid. For example, the projection surface maydefine the surface where the optical aid to be used later is to bepositioned with respect to the user's eyes. The projection surface maybe defined within the volume of the optical aid as well as outside it.The projection surface may be a flat plane, a spherical surface, a toricsurface, or any other surface inbetween the user's retina and the visualfield. The surface may be virtual/virtually, for example not associatedwith a surface of an entity.

The projection surface can be positioned outside of the eyes, forexample, when the projection surface is a spectacles plane, where thelenses of spectacles are placed or the surface can be a screen plane oroptics plane of the virtual/augmented/mixed reality headset or glasses.It may then be fixed in a coordinate system of a head. The projectionsurface can also be positioned on the surface of the eye or inside ofthe eye, which is the case for a contact lens or ophthalmic implant. Theprojection surface on the surface of the eye may be linked to the headcoordinate system, while the eye(s) of the user may move in relation tothe projection surface. This is the case of a segmented bifocal ormultifocal contact lens, which remains in place even when the eye(s) ofthe user move.

In an example, the contact lens as well as ophthalmic implant may movetogether with the eye and the eye projection surface is fixed at thecoordinate system of the eye(s). Since an individual coordinate systemmay be assumed for each eye, the projection surface may be individualfor each eye.

Further, the projection process can be equally applied to thehead-centred projection surface, as well as eye-centred projectionsurface.

In one example, projection may take into account individualcharacteristics of the user. These may include interpupillary distances,shape of the face/nose which may affect position and angle of thespectacles plane on the head, geometry and parameters of the eyestructures, such as corneal curvature, range of the pupil size, positionof the natural lens, length or other dimensions of the eye, etc.

Additionally or alternatively, projection may incorporate furtheroptical parameters of the user's eye(s) which may be influenced by thevisual field. These may include eye rotation in the orbit, adjustment ofthe pupil size to the illumination level of the visual field,accommodation of the natural lens to bring visual field in focus,closing and/or opening of the eye lid.

Projection may be performed by ray tracing, when the path of light fromobjects of the visual field is traced based on physical rules of thelight propagation. Preferably, the light may be traced from the objectuntil reaching the retina of the user.

Propagation of light from the object through the projection surface onthe way to the retina may define the locus of object on the projectionsurface. The projection may be formed by the rays reaching the retinaand forming the image on the retina.

The projection may be performed with simplified methods of mathematicaland geometrical transformations.

Mapping may be performed by geometric projection: relating coordinatesof the visual scene to the coordinates on the projection surface. Forexample, position of the centre of a smartphone display in the visualfield may be translated into the position of the point in a spectaclesplane. Additionally or alternatively, limiting optics may be taken intoaccount for mapping. For example, the pupil size may affect the activearea of contact lenses, corneal implants and/or intraocular lenses. Whenthe pupil is constricted, light can reach retina through central zone ofthe visual aid only, while a dilated pupil may increase an aperture ofthe visual aid and involves peripheral optical zones of the lens. Thisrelation may be considered for customization of multifocal lenses, whichhas the optical power changing with distance from the centre. Forexample, the user may be mainly utilizing distance vision in theoutdoor, well lid conditions, while utilizing near vision indoors withrelatively limited illumination. The pupil-constricted mapping mayproduce a mix of near and far distances (and corresponding opticalpowers) in the central zone of the visual aid, since in both near andfar activities light passes through a central zone.

The near distance activity associated with limited illumination may alsobe mapped on the concentric peripheral zones.

In this case customization can be achieved by optics facilitatingdistance vision in the centre, matching the conditions of constrictedpupil in the outdoor setting, and placing optics facilitating nearvision in the periphery in such a way that near zone opens when pupildilates in the low light conditions.

Customisation may take into account the performance of the opticalsystem of the eye and defocus tolerance based on the eye geometry. Withthe constricted pupil the depth of focus may be increased, which mayenhance the range of distances formed in focus at the retina. Thus therequirement of optical power accuracy in the central zone of the visualaid may be lower than in the peripheral zones.

Mapping may combine measurements performed during multiple visiontasks/activities. It can be envisaged that user is performingmeasurements continuously, effectively combining typical daily visiontasks.

The system may be a head mounted wearable adapted to be worn by theuser. In particular, the wearable may be a single module comprising allthe elements or sensor devices/units of the system. Thus, the visualfield sensor and the head orientation and/or position sensor may be inthe same housing.

Thus, the system may be compact and reduced in power consumption aswell.

Coordinate systems of the respective head orientation and/or positionsensor and the respective visual field sensor may be aligned. Inconsequence, a coordinate transformation may be avoided. Computationalsteps can be reduced consequently.

The coordinate systems of the respective head orientation and/orposition sensor and the respective visual field sensor may be the sameor may have a same reference point. Thus, only rotational informationmay be needed for transforming the one into the other.

The visual field sensor and the head orientation and/or position sensormay be separated from each other.

In consequence, the system may be provided in modular form. For example,the visual field sensor may be operated or deposited at a desk, a shelf,a board or another deposit. The head orientation and/or position sensormay be head mounted instead. Thus, in order to not have a bulky deviceat the head, the system can be provided modularly in this way.

In a modular implementation of the system, the visual field sensor maybe mounted on a body part of the user, different from a head, forexample a torso, while the head orientation and/or position sensor maybe head mounted.

Measurements of the visual field sensor and head orientation and/orposition sensor may be synchronised in order to correctly link headorientation and/or position to the objects of the visual field.Synchronisation may be performed in a real time of the measurements, bytriggering or reading out the measurements of both sensorssimultaneously or within a predefined time period which may be(negligibly) small. Synchronisation may be performed by recordingmeasurements of both sensors independently, but with informationallowing to link the recorded measurements to the time. For example, ina modular implementation, the visual field sensor and head orientationand/or position sensor may have an onboard clock, which can be relatedto the common time point, and the measured data is recorded togetherwith corresponding timestamp. On the processing stage the measurementsof both sensors may be linked to the common time system.

The same applies to the context sensor: it may be synchronised withother sensors in real-time or may have an independent clock, which canbe related to the common time point.

The head orientation and/or position sensor may be coupled to the visualfield sensor. The head orientation and/or position sensor may be adaptedto provide positioning information of the visual field sensor totransform positioning information from a coordinate system of the headorientation and/or position sensor into a coordinate system of the headorientation and/or position sensor. The transformation may be performedby the processing unit. Thus, the processing unit and the headorientation and/or position sensor may be in communication with eachother. This communication may be direct via a cable or indirect viacommunication means such as an antenna system driven short rangecommunication system, such as Bluetooth or wireless local area network(WLAN). The head orientation and/or position sensor may thus have aninterface for connecting to a standard WLAN device. This interface maybe shared by the head orientation and/or position sensor and/or theprocessing unit. The position of the processing unit may be within asingle device together with at least the head orientation and/orposition sensor. Inside the single device, the visual field sensor maybe located as well. However, the processing unit may be provided as aseparate unit. For example, the processing unit may be provided via anetwork on a (foreign) server or over the cloud. Thus, the processing bythe processing unit may be performed on a device which is only incommunication with at least one of the other elements of the system,such as an interface of the system for communication or for connectingcommunication means to the system.

The projection surface may be associated with and/or linked to anoptical aid.

For example, the projection surface may be a plane at which the opticalaid is to be positioned or used later. Thus, the projection surface maybe the plane of the optical aid. The optical aid may for example bespectacles, a lens, or a surface of the eyes.

In consequence, optical powers and pupil diameters may be considered atspecific distances from the user's eyes.

According to a second aspect, a use of the system according to the firstaspect is provided. The optical parameter distribution on the projectionsurface is used for customization of an optical aid. The opticalparameter may be at least one of optical powers, pupil diameters, depthsof focus, spectral content of light, angular distribution of light, andpolarization state of light. The optical parameter distribution maycomprise a distribution of optical parameters on the projection surface.

The optical parameter distribution on the projection surface to be usedlater for the optical aid may comprise a combination of both the pupildiameter and the optical powers. Thus, illumination requirements andpower requirements of the individual can be taken into accountsimultaneously.

Pupil diameter/size may be estimated from illumination conditions, suchas intensity and spectral content of light using empirical formulasand/or models. Such formulas may include other parameters of theenvironment as well as personalized coefficients. Models may be generalor personal. Pupils diameter/size may be further used to calculate depthof focus of vision. Depth of focus may be used to optimise customizationof optical aid.

When a number of activities have been recorded requiring differentoptical powers with different depth of focus, a combined solution can befound by combining optical powers and depth of focus. For example, anactivity A is performed at the distance 1 m in the bright illumination.This leads to an optical power requirement of 1D and depth of focuscorresponding to constricted pupil, which may be 0.5D, so the range ofoptical powers is 0.75-1.25D. For example, an activity B is performed atdistance 1.25 m at low light and thus the required optical power is 0.8Dand the depth of focus corresponds to constricted eye, which is around0.1D, so the range is 0.75-0.85D. Since the customization of the opticalaid should be able to provide best vision for the most of the visualactivities, the acceptable power range may be 0.75-0.85D, which wouldsatisfy requirements of both activities A and B.

According to a third aspect, a method for determining an opticalparameter distribution at a projection surface is provided. The methodcomprises measuring, by a visual field sensor, a visual field of a userrelated to a specific vision task. This may include identifying, by thevisual field sensor, an object related to the specific vision task inthe visual field of the user. The method further comprises determining,by the visual field sensor, gaze directions of the user during thespecific vision task. The method further comprises measuring, by a headorientation and/or position sensor, head orientation and/or position ofthe user in relation to the visual field during the specific visiontask, e.g. head angles of the user associated with the gaze anglesduring the specific vision task. The method may comprise enablingcomputation of the user's eye orientation in relation to the head of theuser based on the gaze directions of the user and the head orientationand/or position of the user to determine an optical parameterdistribution at a projection surface between the visual field and aretina of the user. For example, the method further comprises enablingcomputation of corresponding differences between the head angles and thegaze angles to determine an optical parameter distribution at aprojection surface between the visual field and a retina of the user.

According to a fourth aspect, a computer program product is providedcomprising program code portions for carrying out a method according tothe second aspect when the computer program product is executed on oneor more processing units.

According to a fifth aspect, a computer program product according to thethird aspect stored on one or more computer readable storage media isprovided.

According to a sixth aspect, an optical aid is provided. The optical aidmay be an adjustable optical aid. The optical aid can be adjusted/isadjustable based on a method according to the third aspect or based onusing a system according to the first aspect.

Even if some of the aspects described above have been described inreference to the system, these aspects may also apply to the method.Likewise, the aspects described above in relation to the method may beapplicable in a corresponding manner to the system.

It is clear to a person skilled in the art that the statements set forthherein under use of hardware circuits, software means or a combinationthereof may be implemented. The software means can be related toprogrammed microprocessors or a general computer, an ASIC (ApplicationSpecific Integrated Circuit) and/or DSPs (Digital Signal Processors).

For example, the sensor unit herein, such as the head orientation and/orposition sensor, the visual field sensor, the processing unit and thecontext sensor may be implemented partially as a computer, a logicalcircuit, an FPGA (Field Programmable Gate Array), a processor (forexample, a microprocessor, microcontroller (pC) or an array processor)/acore/a CPU (Central Processing Unit), an FPU (Floating Point Unit), NPU(Numeric Processing Unit), an ALU (Arithmetic Logical Unit), aCoprocessor (further microprocessor for supporting a main processor(CPU)), a GPGPU (General Purpose Computation on Graphics ProcessingUnit), a multi-core processor (for parallel computing, such assimultaneously performing arithmetic operations on multiple mainprocessor(s) and/or graphical processor(s)) or a DSP.

It is further clear to the person skilled in the art that even if theherein-described details will be described in terms of a method, thesedetails may also be implemented or realized in a suitable device, asystem, a computer processor or a memory connected to a processor,wherein the memory can be provided with one or more programs thatperform the method, when executed by the processor. Therefore, methodslike swapping and paging can be deployed.

It is also to be understood that the terms used herein are for purposeof describing individual embodiments and are not intended to belimiting. Unless otherwise defined, all technical and scientific termsused herein have the meaning which corresponds to the generalunderstanding of the skilled person in the relevant technical field ofthe present disclosure; they are to be understood too neither too farnor too narrow. If technical terms are used incorrectly in the presentdisclosure, and thus do not reflect the technical concept of the presentdisclosure, these should be replaced by technical terms which convey acorrect understanding to the skilled person in the relevant technicalfield of the present disclosure. The general terms used herein are to beconstrued based on the definition in the lexicon or the context. A toonarrow interpretation should be avoided.

It is to be understood that terms such as e.g. “comprising” “including”or “having” etc. mean the presence of the described features, numbers,operations, acts, components, parts, or combinations thereof, and do notexclude the presence or possible addition of one or more furtherfeatures, numbers, operations, acts, components, parts or theircombinations.

The term “and/or” includes both combinations of the plurality of relatedfeatures, as well as any feature of that plurality of the describedplurality of features.

In the present case, if a component is “connected to” or “incommunication with” another component, this may mean that it is directlyconnected to or directly accesses the other component; however, itshould be noted that another component may be therebetween. If, on theother hand, a component is “directly connected” to another component or“directly accesses” the other component, it is to be understood that nofurther components are present therebetween.

Other objects, features, advantages and applications will becomeapparent from the following description of non-limiting embodimentsregarding the accompanying drawings. The same or similar components arealways provided with the same or similar reference symbols. In thedescription of the present disclosure, detailed explanations of knownconnected functions or constructions are omitted, insofar as they areunnecessarily distracting from the present disclosure. In the drawings,all described and/or illustrated features, alone or in any combinationform the subject matter disclosed therein, irrespective of theirgrouping in the claims or their relations/references. The dimensions andproportions of components or parts shown in the figures are notnecessarily to scale; these dimensions and proportions may differ fromillustrations in the figures and implemented embodiments. In particular,in the figures, the thicknesses of lines, layers and/or regions may beexaggerated for clarity.

FIG. 1 schematically illustrates a scenario where a system fordetermining an optical parameter distribution at a projection surface isused;

FIG. 2 schematically illustrates a method for determining an opticalparameter distribution at a projection surface;

FIG. 3 schematically illustrates point clouds in a coordinate system ofa user's head;

FIG. 4 schematically illustrates a coordinate system of the head andmapping of the object in sagittal plane into the spectacles plane;

FIG. 5 schematically illustrates a requirement for power distribution inform of a power map at an optical aid's plane corresponding to the righteye;

FIG. 6 schematically illustrates a possible implementation of a powerdistribution/profile of an optical aid as an example of progressiveaddition spectacles lens;

FIG. 7 schematically illustrates an example of a power profile; and

FIG. 8 schematically illustrates a projection of pupil diameters at anoptical aid's plane.

The system and the method will now be described with respect to theembodiments. In particular, without being restricted thereto, specificdetails are set forth to provide a thorough understanding of the presentdisclosure. However, it is clear to the skilled person that the presentdisclosure may be used in other embodiments, which may differ from thedetails set out below.

FIG. 1 schematically illustrates a scenario 100 where a system fordetermining an optical parameter distribution at a projection surface isused. At least part of the system is arranged in the device 110. Thedevice 110 may include a head orientation and/or position sensor. Inparticular, the head orientation and/or position sensor in FIG. 1 can beone dimensional due to the sagittal view of the illustrated head 150.The head orientation and/or position sensor measures the head's 150orientation in the sagittal plane as shown in FIG. 1. However, this maybe extended to all planes with the respective sensor equipment insidethe head orientation and/or position sensor of the device 110. So, thehead orientation and/or position sensor may be calibrated to measure ahead angle β=0 when the head does not tilt with respect to thehorizontal. This is specifically shown in FIG. 1.

When viewing of objects requires a gaze angle (α) below the horizontalplane of the eyes 170, the head inclination (β) (also referred herein ashead angle) is only partially contributing to the gaze angle (α). Theremainder (γ) comes from reorienting the eyes 170 (only eyes' 170inclination) with respect to the head's inclination β. This is performedby the body itself in order to reduce the load on the neck 160. Thedistribution of angle contributions between head 150 and eyes 170 isindividual and also depends on the individual position of the object 130which may be specific to the activity and user. The object 130 in FIG. 1is a handheld media and is looked upon by the user, illustrated by thehead 150. The device 110 may be worn by the user, in particular at theuser's head or the user's temple. Further to this, the device 110 may bea head mounted wearable. The device 110 may be integrated into aspectacles frame or mountable thereon.

Further to the head orientation and/or position sensor, the device (e.g.wearable device) may incorporate at least one distance sensor, which isable to measure distances to the object 130 in the visual field 120. Thevisual field 120 is indicated by the arrows and stars in FIG. 1. Thedistance sensor may be part of the visual field sensor described hereinor the visual field sensor may be in the form of a distance sensordescribed with respect to FIG. 1. Since the head and the body of healthyindividuals are rarely in complete rest during an awake state, adistribution of head inclination angles is expected during a period ofobservation. With the distance sensor performing multiple measurementsseparated in time it is possible to obtain distances to the object 130within the visual field 120 in various directions from an observationpoint (head's view). This may be the reference of the head coordinatesystem.

Sampling of the environment (the visual field 120) may be performed byat least one directional distance sensor. The distance sensor may be awearable distance sensor coaligned with the head of the user and/orintegrated in the device 110. The distance sensor may have scanningmeans or angle/space resolved sensor, however, the distance sensor mayalso exclusively rely on natural head movements of the user in order tosample the environment in different directions or may be a combinationof different means of sampling in different directions. By relatingdistance measurements to the orientation or position of the device 110it is possible to construct a two or three dimensional point cloudrepresenting an environment in relation to the head orientation and theposition of the user. Initial orientation or position of the device 110may be obtained from inertial (e.g. accelerometer, gyroscope,magnetometer) sensors or location sensors incorporated in the device110.

In order to automatically identify activities, additional contextsensors can be used. For example, a motion sensor can sample user'smotion intensity and statistical characteristics. For example, specificsignature movements can be recognized, for example a movement of thehead 150 while reading. The context sensor(s) may also be included inthe device 110.

Activities may be automatically identified with help of external sensorsor with direct user input performed via user interface as a part of thewearable and/or system and/or additional device, such a mobile phone orinternet interface. The input identifying activity can be performed inreal time or later. For example, the user might be able to reviewhistory of measurements via interactive interface implemented as a webpage or mobile application and link time series to specific activities.

An example of such input can be: from 10:00 till 10:30 activity wasReading, from 10:30 till 10:45 activity was Walking, from 10:45 till11:45 activity was Driving and so on.

Identification of activities can also be performed as a combination ofautomatic and manual input. For example, the system may only requestuser input when the confidence or other metric of performance ofautomatic identification is below certain threshold. In the exampleabove, the system may be able to automatically identify Reading andDriving (confidently), but may have some concerns regarding Walking andthus may request a user input. The system may be further configured touse user input on the single episode of activity to update automaticidentification of other episodes. In the example above, the user maymanually specify the single episode of Walking between 10:30 and 10:45and the system may automatically update the activity classifier andre-evaluate all remaining episodes.

The head orientation and/or position sensor may comprise anaccelerometer. In the simplest case the single axis accelerometer may beused which is capable of measuring projection of acceleration vector ona single axis. The single axis of the accelerometer can be alignedhorizontally with the device 110 in such a way that when the user islooking straight forwards (β=0), the accelerometer measures zeroacceleration, since the projection of vector g (gravitationalacceleration) on axis x is zero (g_(x)=g sin β=0, g is an absolute valueof vector g). When the head 150 of the user is tilted forwards (β>0)projection g_(x) becomes positive. The head inclination angle β can becalculated from the measured projection yielding β=arcsin g_(x)/g. Theaccelerometer sensor can measure acceleration along the axis z acting onthe device 110 (head orientation and/or position sensor coordinatesystem). In the absence of significant acceleration of the device 110caused by motion (which is expected during important visual activities)the accelerometer measures gravitational force and thus acceleration g.

The vertical angle (pitch) of the head β can be derived from themeasurements of gravitational force by the accelerometer (at least oneaxis) mounted on the head 150 (for example on spectacles or at thetemple of the user). In a more advanced configuration the headorientation and/or position sensor may include a 3-axis gyroscope, a3-axis accelerometer and a 3-axis magnetometer (for example a compass).Then it is possible to estimate absolute angles of the head orientationand/or position sensor and, correspondingly, absolute orientation of thehead 150, when the head orientation and/or position sensor is fixed tothe head 150 of the user.

Additionally or alternatively, the head position sensor is capable ofmonitoring the position of the head in relation to the visual filed orvison field sensor.

A position of the object 130 of interest (object related to a specificvisual activity) can be found by observing the visual field 120 with thevisual field sensor in relation to the axes of the head 150. Forexample, this can be performed by a head mounted camera, also calledpoint-of-view (POV) camera, a POV distance sensor or a space-resolveddistance sensor (3D camera). By detecting object(s) of interest in thevisual field it is possible to indirectly derive angles (α, β, γ) andpositions (x, y, z) of the alignment of the object(s) in the visualfield.

In combination with distances measured by the distance sensor, thepositions of points can be obtained in the sagittal plane of the bodyand form a point cloud (points in FIG. 1 of visual field 120) of anobject 130 in the visual field 120. Further, the recognition of theobject 130 can be performed based on the expected visual field 120 ifthe type of vision task is already given (for example, if the user hasprovided information via a user interface) or the type of activity canbe recognized automatically by comparing statistics of measureddistances (obtained by the visual field sensor/distance sensor) with adataset of statistical signatures of visual activities.

For example, the identified or recognized activity is reading fromhandheld device 130, as in the example shown in FIG. 1. In this case theprimary object of visual activity is reading the handheld device 130,which has a flat surface and thus would appear as a line in the sagittalplane projection in the comfortable arm reach distance. Pointscorresponding to such a definition are marked with a dashed line (seeFIG. 1). The angles corresponding to the points on the object 130 ofprimary visual activity are further defining the set of gaze angles αused by the user to perform the corresponding vision task. Since theangle β of head inclination is known from head orientation and/orposition sensor mounted on the head 150 it is possible to estimate eyes'170 shifts/angles γ=α−β.

The density of the point cloud and the scanning range can be increasedby adding further distance sensors with orientation and/or positionsdifferent from the visual field sensor or by using sensors which areable to obtain samples in the plurality of directions. For example,these sensors may have a single emitter and plurality of sensitivezones/detectors, with different sensitivity to distance in differentdirections. This can be achieved by sensor design or with additionalelements, for example with optical elements if the sensor is opticallybased.

For example, this is implemented by a laser ranging sensor having a16×16 array of single-photon avalanche diodes (SPAD), which can beconfigured to select a required region of interest. This implements asingle emitter-multiple detectors strategy.

Another example may incorporate a camera or an array of detectorsarranged in such a way that they detect light coming from differentgeometrical positions or/and directions.

In a further example, the distance sensor may have at least one detectorand a plurality of emitters configured to emit light to differentdirections and/or positions. In this case the detector is configured todetect light emitted by at least one of the emitters and reflected fromthe visual field 120. The configuration/arrangement of active emittersmay change from one time point to another, which allows collectingspatially resolved information.

In another example, at least one emitter can be configured to change thedirection of emitted light in order to probe the visual field 120 atdifferent directions/positions.

This can be achieved, for example, by a scanning element, which can be ascanning mirror, scanning prism or other moving optical elementconfigured to modify the optical path of emitted light in order to emitprobing light in different directions. The detector may then beconfigured to detect light reflected from objects probed by emitterradiation. The signal of detector can be linked to the information aboutthe probed direction/position in order to reconstruct the visual field120. These directions may be known a priory from a design of thescanner, obtained in the calibration step or obtained during a scan withadditional feedback signal.

Alternatively, the visual field can be monitored by the visual fieldsensor when physically/mechanically decoupled from the head orientationand/or position sensor and head. For example, the visual field sensorcan be mounted on the body of the user (e.g. on a torso and/or chest) orit can be mounted outside of body (e.g. on a desk or on a dashboard of acar). The head orientation and/or position sensor and the visual fieldsensor may have means of relating coordinate systems of each other, inparticular orientations and/or positions to each other. For example,this can be achieved with additional orientation and/or positionsensor(s) mechanically coupled to the visual field sensor.

Another approach may be limiting relative movement of visual fieldsensor and head. For example, by mounting visual field sensor at aspecific part of the body, different from the head, for example at thechest, in such a way that relative movements of visual field sensor anda head can only be caused by the head inclination, e.g. pitch, yaw,roll, which can be monitored with the head orientation and/or positionsensor.

More details and aspects are mentioned in connection with theembodiments described above or below. The embodiment shown in FIG. 1 maycomprise one or more optional additional features corresponding to oneor more aspects mentioned in connection with the proposed concept or oneor more embodiments described below (e.g. FIGS. 2-8).

FIG. 2 schematically illustrates a method for determining an opticalparameter distribution at a projection surface. The method may as afirst step include classifying S210 the visual task. Thereafter, themethod comprises measuring S220, by a visual field sensor, visual fieldof a user related to a specific vision task. This may includeidentifying an object related to the specific vision task in the visualfield of the user. The method further comprises determining S230 gazedirections of the user during the specific vision task. The methodfurther comprises measuring S240, by a head orientation and/or positionsensor, head orientation and/or position of the user in relation to thevisual field during the specific vision task. The method furthercomprises enabling S250 computation of the user's eye orientation inrelation to a head of a user based on the gaze directions of the userand the head orientation and/or position of the user to determine anoptical parameter distribution at a projection surface between thevisual field and a retina of the user.

In particular, the method may be performed in two different ways. Thefirst way is based on mechanically coupled visual field sensor, like thedistance sensor as described with respect to FIG. 1, and headorientation and/or position sensor. The method as shown in FIG. 2 maytherefore comprise at least one of the following (additional) stepsaccording to the first way of performing the method:

-   -   obtaining S205 a point cloud of one or more objects in a visual        field of a user;    -   classifying S210 the type of a vision task;    -   identifying S220 at least one relevant object related to a        specific vision task in the visual field by the visual field        sensor; and    -   calculating S230 at least one of the components of a gaze angle        (pitch, yaw and/or roll in a common coordinate system)        corresponding to at least one relevant object of vision task;    -   measuring S242 (S240) a head orientation by a head orientation        and/or position sensor during the visual activities;    -   calculating S244 (S240) at least one component of the head angle        (pitch, yaw and/or roll in the common coordinate system); and    -   calculating S250 at least one angle between a head and objects        (eyes' angles) as the difference between the gaze direction and        head orientation and/or position

Recognition of the objects is easier to perform in the geocentriccoordinate system, since objects of the visual activity are oftenarranged in the real space in relation to the gravitational field, forexample, papers on the desk, computer displays, screens of televisionsets, dashboards of the car.

The second way is based on a mechanically decoupled visual field sensorand head orientation and/or position sensor. The method as shown in FIG.2 may therefore comprise at least one of the following (additional)steps according to the second way of performing the method:

-   -   identifying S220 one or more objects in a visual field of the        user by a visual field sensor and calculating S230 a gaze angle        (in the common coordinate system)    -   measuring S240 a head orientation by a head orientation and/or        position sensor during the visual activities and calculating the        head angle (in the common coordinate system)    -   calculating S250 at least one angle between the head and objects        (eyes' angles) as the difference between the gaze angle and head        angle.

More details and aspects are mentioned in connection with theembodiments described above or below. The embodiment shown in FIG. 2 maycomprise one or more optional additional features corresponding to oneor more aspects mentioned in connection with the proposed concept or oneor more embodiments described above (e.g. FIG. 1) or below (e.g. FIGS.3-8).

FIG. 3 schematically illustrates point clouds in a coordinate system ofa user's head. In particular, a sagittal plane is shown forcomprehensiveness. Points cloud can be obtained by combiningmeasurements of at least single-directional distance sensor with themeasurements of orientation and position of the sensor. Measurementsfrom multiple distance sensors (for example, probing differentdirections) can be combined in one map, or can form multiple maps. Whenat least a pitch angle of the head inclination is measured, pointsclouds are defined in the two dimensional sagittal plane. With the useof additional orientation sensors, such as gyroscope and/ormagnetometer, it is possible to add yaw and roll angles of the head anddefine points clouds in three-dimensional space. For example, byclassifying the visual task or activity, gaze angles can be extractedaccordingly. In the sagittal plane, the points corresponding torespective gaze angles are all lying in particularly the same distancefrom the head U depending on the visual task. FIG. 3 shows points cloudcorresponding to near vision (NV) task, such as reading a book orlooking on the smartphone, in this example at the distance around 0.33m, corresponding to 3D refraction, another cloud is in the intermediatevision (IV) zone around 1 m (1D refraction), which could be viewingdesktop computer display and cloud in far vision (FV) zone around 2meters (0.5D), which could be watching TV.

Point clouds may be forming patterns characteristic to the activity.Shape and/or position of point clouds may be used to classify visualactivities automatically. The classification may be in combination witha user input of what type of visual task the user performs and/or incombination with pattern recognition from a video taken during thevisual task and/or in combination with measurements of the othersensors. For example, the visual field sensor may be a camera, and theprocessing involves finding objects from 2D images, for example,identifying books or handheld devices (smartphones or tablets), computerscreen. This involves understanding of user's activities by cameraimages.

More details and aspects are mentioned in connection with theembodiments described above or below. The embodiment shown in FIG. 3 maycomprise one or more optional additional features corresponding to oneor more aspects mentioned in connection with the proposed concept or oneor more embodiments described above (e.g. FIGS. 1-2) or below (e.g.FIGS. 4-8).

FIG. 4 schematically illustrates a coordinate system of the head andmapping of the object in sagittal plane into the spectacles plane.Placing of objects in sagittal plane can be assumed when the activity isbilaterally symmetrical. Examples of such activities include reading thehandheld media, such as a book, working on a desktop computer, workingon workbench, etc. In this case the distances to the objects may bemonitored together with head's pitch angle without regard to yaw androll. Example can be activities presented in FIG. 3.

The respective coordinates of points of the point cloud (here point A)associated with the specific visual task are recalculated to thecoordinate system of the head. In particular, optical parameters, suchas the optical power, are mapped to a projection surface, which may be aspectacles' plan.

FIG. 4 specifically illustrates the following numerals:

P_(xz)—spectacles plane;

P_(yz)—sagittal plane;

P_(xy)—perpendicular plane to P_(xz) and P_(yz);

P—eye pupil position;

A—point of the object;

A_(s)—image of object point on the spectacle plane;

O—root of the nose;

O_(s)—projection of O on spectacles plane;

OO_(s)—vertex distance; and

OP distance—monocular pupillary distance adjusted to vergence.

Further, a panoscopic tilt (lens pitch) and wrap angle (lens yaw) can betaken into account for customizing the specific optical aid.

In a more general case of activity, the bilateral symmetry cannot beassumed (e.g. during car driving). In this case monitoring of headorientation can be performed in all three angular dimensions: pitch, yawand roll. The points cloud is not limited to sagittal plane and definedin the 3D space. The illustrated geometrical model can be furtherextended to allow rendering to the projection surface.

More details and aspects are mentioned in connection with theembodiments described above or below. The embodiment shown in FIG. 4 maycomprise one or more optional additional features corresponding to oneor more aspects mentioned in connection with the proposed concept or oneor more embodiments described above (e.g. FIGS. 1-3) or below (e.g.FIGS. 5-8).

FIG. 5 schematically illustrates a requirement for power distribution inform of a power map at an optical aid's plane corresponding to the righteye. For example, such distribution can be obtained from points cloudsin FIG. 3 with geometrical transformation shown in FIG. 4. In this casethe near vision (NV) zone yields a requirement to optical aid of havinga zone with optical power of 3D to help user see an object at distance0.33 m. The intermediate vision (IV) zone which may be viewing desktopdisplay is producing zone corresponding to zero pitch of the opticalpower of 1D (distance of 1 m). Finally, the far vision zone (R) withoptical power below 1D (from 1 m to infinity) can be found above IVzone.

The NV zone is illustrated to be slightly right from the middle. This isdue to a rotation of the eyes in a rotation direction to the nose of theuser when reading (convergence). FIG. 5 thus illustrates a right eyespectacle's lens customization for a user with presbyopia. The zones canbe customized to the user's needs. As can be seen from FIG. 5, theoptical powers may be distributed in a non-uniform manner respectively,whereby the zones' transitions may be smooth as well.

Consequently, an optimised lens power mapping based on personal visualbehaviour may be provided.

More details and aspects are mentioned in connection with theembodiments described above or below. The embodiment shown in FIG. 5 maycomprise one or more optional additional features corresponding to oneor more aspects mentioned in connection with the proposed concept or oneor more embodiments described above (e.g. FIGS. 1-4) or below (e.g.FIGS. 6-8).

FIG. 6 schematically illustrates a possible implementation of a powerdistribution/profile of an optical aid as an example of progressiveaddition spectacles lens. The optical aid in FIG. 5 is a lens having around shape, from which the lens for fitting in spectacles may be cutalong the dashed line. Since the required power zone profile shown inFIG. 5 cannot be implemented with a lens, the customization step isrequired to find a feasible design which accounts for the opticalrestrictions of the spectacle lens and matches desired profile as closeas possible. Modern progressive additional lenses feature blendingregions (BR) which are not usable for the good vision due to highastigmatism. They are required to blend the optical powers of lenses forfar and near visions. The optical power gradually changes from distancereference point (DRP) for far vision to the near reference point (NRP)for near vision along the progressive corridor. This progression isdefined by power profile. Power profile along with other parameters canbe optimised to fit the required distribution.

More details and aspects are mentioned in connection with theembodiments described above or below. The embodiment shown in FIG. 6 maycomprise one or more optional additional features corresponding to oneor more aspects mentioned in connection with the proposed concept or oneor more embodiments described above (e.g. FIGS. 1-5) or below (e.g.FIGS. 7-8).

FIG. 7 schematically illustrates an example of a power profileimplementing design fitting required power map from FIG. 5 with theprogressive addition lens layout from FIG. 6. These measurements maycorrespond to the distance measurements in the sagittal plane inaccordance with FIG. 3. Optical power in this case is calculated as areciprocal of the distance to the object of visual task. The eye pitchangle is calculated from the gaze angle on the FIG. 3 and measured headangles. These measurements may be extended to different planes. In theparticular example, pitch of angle smaller than −5 degrees implementsfar distance vision, starting from DRP.

At the pitch around 0 the power equals to 1D (distance of 1 m,corresponding to example of desktop display in FIG. 3). With furtherincrease in pitch angle profile reaches NRP with power of +3D (0.33 m),corresponding to handheld media in FIG. 3.

More details and aspects are mentioned in connection with theembodiments described above or below. The embodiment shown in FIG. 7 maycomprise one or more optional additional features corresponding to oneor more aspects mentioned in connection with the proposed concept or oneor more embodiments described above (e.g. FIGS. 1-6) or below (e.g. FIG.8).

FIG. 8 schematically illustrates a projection of pupil diameters at anoptical aid's plane. In particular, light intensity/luminance and/orlight spectral content may be measured by the visual field sensor andconverted into the pupil size of the user using empirical formulas andmodels. Thus, the optical aid can be designed for different lightintensity exposures of the user as well. The eye is known to accommodatedifferently in different lightning conditions. For example, inparticular dark settings eye accommodates only between 0.5 and 2 meters(2 to 0.5 D, correspondingly). The depth of focus (the range of opticalpowers which are imaged on retina with sufficient quality) is inverselyproportional to the pupil diameter, which means that in highlyilluminated settings, the pupil constricts and the range increases. Thedepth of focus changes from 0.1D to 0.5D. This can be taken into accountin the design of optical aid. In the example of FIG. 8 the pupil islarger for the lower zones, which means that the depth of focus would bereduced in these zones. This may be used to define the accuracyrequirements to the map of optical powers of the visual aid, like theone shown in FIG. 5. In this example, the design of optical aid shoulddeliver the optical power in the lower zones (used for near vision inthis example) with high accuracy. In this example the upper zones aretypically used with the pupil size decreased and thus depth of focus isincreased which leads to the higher tolerance to defocus in this area.Thus there is a higher flexibility for the selection of optical powersof far distances located in the upper zones in this particular case.

More details and aspects are mentioned in connection with theembodiments described above or below. The embodiment shown in FIG. 8 maycomprise one or more optional additional features corresponding to oneor more aspects mentioned in connection with the proposed concept or oneor more embodiments described above (e.g. FIGS. 1-7).

The example of the spectacles plane in FIG. 6 illustrates the case whenvisual aid is decoupled from the eyes and thus movement of the eyes maybe associated with changes in the optical power of visual aid.

Another example of visual aid may represent contact lenses, cornealimplants and/or intraocular lenses, which are moving with the eye. Inthis case the projection surface is always aligned with the gaze andhead orientation is irrelevant. Nevertheless, the method allows to mapthe objects in the peripheral vision to the projection surface. A flowchart as illustrated in FIG. 2 may represent various processes,operations or steps, which may, for instance, be substantiallyrepresented in computer readable medium and so executed by a computer orprocessor, whether or not such computer or processor is explicitlyshown. Methods disclosed in the specification or in the claims may beimplemented by a device having means for performing each of therespective acts of these methods.

It is to be understood that the disclosure of multiple acts, processes,operations, steps or functions disclosed in the specification or claimsmay not be construed as to be within the specific order, unlessexplicitly or implicitly stated otherwise, for instance for technicalreasons. Therefore, the disclosure of multiple acts or functions willnot limit these to a particular order unless such acts or functions arenot interchangeable for technical reasons. Furthermore, in some examplesa single act, function, process, operation or step may include or may bebroken into multiple sub-acts, -functions, -processes, -operations or-steps, respectively. Such sub acts may be included and part of thedisclosure of this single act unless explicitly excluded.

The aspects and features mentioned and described together with one ormore of the previously detailed examples and figures, may as well becombined with one or more of the other examples in order to replace alike feature of the other example or in order to additionally introducethe feature to the other example.

Furthermore, the following claims are hereby incorporated into thedetailed description, where each claim may stand on its own as aseparate example. While each claim may stand on its own as a separateexample, it is to be noted that—although a dependent claim may refer inthe claims to a specific combination with one or more other claims—otherexamples may also include a combination of the dependent claim with thesubject matter of each other dependent or independent claim. Suchcombinations are explicitly proposed herein unless it is stated that aspecific combination is not intended. Furthermore, it is intended toinclude also features of a claim to any other independent claim even ifthis claim is not directly made dependent to the independent claim.

1. A system for determining an optical parameter distribution at aprojection surface, the system comprising: a visual field sensorconfigured to measure a visual field of a user related to a specificvision task and further configured to determine gaze directions of theuser during the specific vision task; and a head orientation and/orposition sensor configured to measure head orientation and/or positionof the user in relation to the visual field during the specific visiontask; wherein the system is configured to enable computation of theuser's eye orientation in relation to the head of the user based on thegaze directions of the user and the head orientation and/or position ofthe user to determine an optical parameter distribution at a projectionsurface between the visual field and a retina of the user.
 2. The systemof claim 1, wherein the visual field sensor is configured to identify anobject of the visual field of the user related to the specific visiontask and configured to derive the gaze directions of the user related tothe identified object of the visual field.
 3. The system according toclaim 1, wherein the system further comprises a context sensorconfigured to measure at least one parameter related to an activity ofthe user.
 4. The system according to claim 1, further comprising astatistical classifier configured to identify the vision task and/orobject of the visual field of the user from at least one of: the visualfield sensor; the head orientation and/or position sensor; and thecontext sensor, where identification is at least in part performedautomatically.
 5. The system according to claim 1, further comprising: amemory unit configured to store the head orientation and/or position andthe gaze directions both related to the specific vision task, whereinthe stored head orientation and/or position and the stored gazedirections form the basis for determining the optical parameterdistribution at the projection surface between the visual field and theretina of the user.
 6. The system according to claim 1, furthercomprising: a processing unit configured to determine the correspondingdifferences between the head orientation and/or position and the gazedirections and to determine the optical parameter distribution at theprojection surface between the visual field and the retina of the user.7. The system according to claim 5, wherein the processing unit isconfigured to determine the corresponding differences between the storedhead orientation and/or position and the stored gaze directions and todetermine the optical parameter distribution at the projection surfacebetween the visual field and the retina of the user.
 8. The systemaccording to claim 1, wherein the system is or is arranged in a headmounted wearable adapted to be worn by the user.
 9. The system accordingto claim 8, wherein the wearable is a single module comprising all theelements of the system.
 10. The system according to claim 8, whereincoordinate systems of the respective head orientation and/or positionsensor and the respective visual field sensor are aligned.
 11. Thesystem according to claim 1, wherein the visual field sensor and thehead orientation and/or position sensor are separated from each other;and/or wherein the projection surface is associated with and/or linkedto an optical aid.
 12. The system according to claim 1, wherein theoptical parameter distribution on the projection surface is used forcustomization of an optical aid, wherein optical parameter being atleast one of: optical powers; pupil diameters; depths of focus; spectralcontent of light; angular distribution of light; and polarization stateof light.
 13. A method for determining an optical parameter distributionat a projection surface, the method comprising: measuring (S220), by avisual field sensor, a visual field of a user related to a specificvision task; determining, by the visual field sensor, a gaze directionsof the user during the specific vision task (S230); measuring (S240), bya head orientation and/or position sensor, head orientation and/orposition of the user in relation to the visual field during the specificvision task; and enabling (S250) computation of the user's eyeorientation in relation to the head of the user based on the gazedirections of the user and the head orientation and/or position of theuser to determine an optical parameter distribution at a projectionsurface between the visual field and a retina of the user.
 14. Acomputer program product comprising program code portions for carryingout a method according to claim 13 when the computer program product isexecuted on one or more processing units, wherein, for example, thecomputer program product is stored on one or more computer readablestorage media.
 15. An optical aid, wherein the optical aid is adjustablebased on a method according to claim 13 or using a system according toclaim 1.